1. Field of the Invention
The present invention relates to an endoscope apparatus which achieves an improvement in observability by easily removing a stain deposited on a surface of an observation window and, more specifically, to a surgical endoscope apparatus.
2. Description of the Related Art
In recent years, surgery using an endoscope has come into widespread use for purposes of minimally invasive medicine. Prevention of deterioration in observation environment caused by deposition of a stain on or generation of a fog on an observation window disposed at a distal end portion of an endoscope presents a challenge to such endoscopic surgery.
In some endoscopes for digestive organs, a fog or a stain is removed by supplying water to a lens at an endoscope distal end portion. A stain deposited on a surgical endoscope may be blood, fat, or the like scattered during surgery, and the stain may not be removed by simply supplying water.
For example, a technique disclosed in Japanese Patent Application Laid-Open Publication No. 2006-55275 has been known as a measure to be taken against the above-described problem.
In the conventional endoscope apparatus, a cover glass serving as an image capture window is attached to a distal end of an inner tube of an insertion portion to face an objective optical system. A coating layer which is a hydrophilically treated layer made of a photocatalyst (e.g., titanium oxide) and having an affinity for water is formed on an outer surface of the cover glass.
When dew condensation occurs on the cover glass due to a difference in temperature from a surrounding environment, the affinity for water of the coating layer diffuses water particles and forms a thin water film, which prevents a fog on the surface. That is, the formation of the water film prevents a fog on the outer surface of the cover glass and returns the cover glass to an initial state, a state in which a clear field of view is ensured. When a stain such as bodily fluids or a splash from a radio knife (not shown) comes into contact with the water film formed on the coating layer of the cover glass, the stain is deposited on the water film.
At the inner tube of the insertion portion, an ultrasonic transducer is provided to be capable of transmitting vibration to the cover glass. When the ultrasonic transducer is driven and controlled, the ultrasonic transducer generates an ultrasonic wave, and the ultrasonic wave is propagated to the cover glass. In the conventional endoscope apparatus, the ultrasonic wave propagated to the cover glass and action of gravity cause the water film formed on the coating layer on the outer surface of the cover glass to drop and be removed. At the time, a stain deposited on the water film drops together with the water film, and the outer surface of the cover glass is cleaned. Note that a water film can also be formed by supplying water onto the coating layer by a water supply nozzle or the like.
However, in the conventional endoscope apparatus, the ultrasonic transducer at the inner tube is attached to a peripheral part, i.e., an inner surface of the inner tube except for a part facing the objective optical system such that the ultrasonic transducer does not interfere with an observation field of view. That is, a region of the observation field of view of an observation window (the cover glass) is separate from the part where the ultrasonic transducer is attached. Depending on the part where the ultrasonic transducer is attached, an ultrasonic wave from the ultrasonic transducer may not be easily transmitted to the region of the observation field of view (an ultrasonic wave propagates with high intensity in a direction perpendicular to the surface where the ultrasonic transducer is attached, and the tendency is especially noticeable in the case of a high-frequency ultrasonic wave), and a stain deposited on the observation window may not be sufficiently removed.